1. Field of the Invention
The present invention relates to an exhaust heat recovery apparatus for recovering the exhaust heat from a heat engine.
2. Description of the Related Art
An exhaust heat recovery apparatus is available that, using a heat engine, recovers the exhaust heat from an internal combustion engine that is mounted on a vehicle, such as a passenger car, a bus and a truck. As an example of the exhaust heat recovery apparatus used for such a purpose, there is the Stirling engine, which is excellent in theoretical thermal efficiency. Japanese Patent Application Publication No. 2005-113810 (JP-A-2005-113810) discloses a Stirling engine used as an exhaust heat recovery device that recovers the thermal energy of the exhaust gas from an internal combustion engine.
The Stirling engine is prepared separately from the internal combustion engine, and is provided on an exhaust gas passage of the internal combustion engine. The exhaust gas passage of the internal combustion engine is constituted of a primary exhaust gas passage that communicates with a heat exchanger of the Stirling engine, and a bypass exhaust gas passage that circumvents the heat exchanger of the Stirling engine. In addition, an exhaust gas flow rate-changing means for protecting the Stirling engine is provided at a divergence point upstream of the primary exhaust gas passage and the bypass exhaust gas passage.
In the meantime, if the Stirling engine is provided on the exhaust gas passage of the internal combustion engine as shown in JP-A-2005-113810, the temperature of the exhaust gas decreases by the time the exhaust gas discharged from the internal combustion engine reaches the heater of the Stirling engine, which is the exhaust heat recovery means. As a result, the power output from the Stirling engine is decreased, and therefore the exhaust heat recovery efficiency drops. Especially, in the exhaust heat recovery apparatus driven by the low-grade heat source, such as the exhaust gas from an internal combustion engine, the drop in the exhaust heat recovery efficiency due to the drop in the temperature of the exhaust gas, which is the heat source, is large. In addition, if the Stirling engine and the internal combustion engine are prepared separately as shown in JP-A-2005-113810, the flexibility in mounting the engines on a vehicle is reduced.